60 INTROGRESSIVE HYBRIDIZATION 



ability instead of the original 1. There would be a hairy- 

 obovate strain and an ovate-glabrous one. Though inter- 

 mediates could be produced and variation might be great in 

 some populations, the chances of ever again attaining the 

 random frequencies of the original population would be ex- 

 tremely small. Even strong artificial selection could scarcely 

 recreate the extreme leaf types 4/0 and 0/4. The popula- 

 tion would now have 2 centers of variation; it would have 

 acquired the necessary minimum differentiation upon which 

 further isolating mechanisms could accumulate. 



